The present invention relates to the field of integrated circuits, and more specifically, to improving the interfacing of integrated circuit in a mixed-voltage environment.
The integrated circuit business and semiconductor industry are continually driven to reduce cost, reduce power, and improve performance. The integrated circuit products include microprocessors, memories, programmable logic, programmable controllers, application specific integrated circuits, and many other types of integrated circuits. Price reduction is strongly driven by migrating products to scaled processes, which reduce die sizes and increase yields. Power reduction has been achieved by circuit design techniques, power management schemes, and parasitic scaling, among other factors. Performance improvement has resulted from design techniques, process enhancements, and parasitic scaling, among other factors.
Process technology is improving. Resulting from the continual scaling and shrinking of device geometries, device sizes and dimensions require the operating voltages to be scaled. Operating voltages have been scaled down from 5 volts to 3.3 volts. This has resulted in the need for mixed-voltage-mode systems. That is, integrated circuits will need to interface with various operating voltages. And, further reductions are expected in the future. This industry provides products and printed circuit boards (PCBs) that utilize both 3.3-volt and 5-volt integrated circuits and devices. It is expected that there may be a considerable transition period for the standard power supply to switch from one voltage level to a lower voltage level.
Process scaling is the dominant method of reducing the die cost. The cost is achieved by receiving higher yields associated with smaller die sizes. Presently, power supply voltages are being reduced as the scaling progresses towards device dimensions that necessitate the reduction of voltage differences across these dimensions.
All manufacturers have not switched over to the lower power supply, simultaneously. Thus the scaling of the operating voltage has resulted in creating a multiple voltage mode industry. Integrated circuit companies must provide products capable of addressing the needs during this intermediate phase before the industry transitions to a single lower power supply voltage. It is expected that this industry will require some time to successfully transition over to the lower power supply.
As can be seen, an improved technique of fabricating, and operating integrated circuits is needed to meet these demands. These integrated circuits should interact with devices that are designed to operate at either the standard or the new lower power supply. The integrated circuit should also provide a cost reduction path to customers that continue to design 5-volt-only systems. Integrated circuits should provide the manufacturer with the flexibility to chase the market to support with a minimum cost and the shortest time to market.
The present invention is a technique of interfacing an integrated circuit in a mixed-voltage mode environment. In particular, the integrated circuit is fabricated using technology compatible with an internal supply voltage level. Externally, the integrated circuit will interface with an external supply voltage level, above the internal supply voltage level. The input and output signals to and from the integrated circuit will be compatible with the internal supply level.
An integrated circuit of the present invention may include on-chip conversion circuit for converting a voltage at a level of external supply voltage to a level of the internal supply voltage, or this internal voltage level may be externally supplied. This internal supply voltage will be used to power the internal devices on the integrated circuit. The integrated circuit will also contain conversion circuitry to convert output signals to be compatible with the external supply voltage. This circuitry may include a level or voltage shifter. Also, the integrated circuit will also be accept input voltages compatible with the external supply voltage. The present invention is a useful technique for providing backward compatibility of a low-voltage process technology.
The present invention may also be used in a separated noisy and quiet supply scheme. For example, an I/O driver may be coupled to a noisy supply while the on-chip conversion circuitry is coupled to the quiet supply. This will provide some isolation from noise at the I/O driver from being coupled to other on-chip circuitry.
Specifically, in one embodiment, the integrated circuit: of the present invention includes a plurality of programmable elements. These programmable elements are programmably configurable to implement logical functions, producing logical signals compatible with a first voltage range, between a first supply voltage and a reference voltage. The integrated circuit further includes a voltage shifter formed on an integrated circuit. The voltage shifter is coupled to convert logical signals from the plurality of programmable elements to logical signals compatible with a second voltage range, between a second supply voltage and the reference voltage. The second supply voltage is above the first supply voltage.
Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, in which like reference designations represent like features throughout the figures.